This invention is concerned with an improved process for upgrading the motor octane number of the low-boiling fraction or components of a gasoline pool.
A significant component of the gasoline pool obtained from processing crude oil is supplied by low-boiling hydrocarbons of the C.sub.5 -C.sub.6 range. These hydrocarbons are normally deficient in terms of octane-number quality. In a typical refining of 50,000 barrels of crude oil, as much as 9000 barrels of low-boiling product may be produced. Common practice, despite the octane deficiency of this material, has been to include it in the gasoline pool and to make up the octane deficiency by use of lead-containing octane-improving additives. For environmental protection reasons, the addition of these additives to gasoline must be drastically limited or prohibited. Consequently, the refiner faces a serious need for an effective means for upgrading the octane number of the low-boiling hydrocarbon fraction or components of his gasoline pool.
Processes for upgrading the octane number of low-boiling hydrocarbons are known, for example see U.S. Pat. No. 2,905,619 and U.S. Pat. No. 3,770,614. Briefly, such processes suffer from disadvantages, including requirements for numerous fractionating steps, recycle streams, and processing stages; n-paraffin elimination (a yield loss) by a sacrificial cracking (shape-selective cracking) of n-paraffins to relatively low-value non-gasoline light gas by-products, and the like. A further notable and undesirable disadvantage is the usual inclusion of the C.sub.6 paraffinic hydrocarbon component in feeds upgraded by conventional reforming operations. While this component may be modestly upgraded through some isomerization in a reforming stage, little, or only a minor portion, of it is converted to aromatic hydrocarbons. Consequently, the inclusion of C.sub.6 paraffin in a reformer feed actually represents a substantial reduction in the efficiency of costly catalyst and reactor facilities.
An object of the present invention, in terms of yield-octane advantages, is to provide a process wherein the low-octane C.sub.5 -C.sub.6 hydrocarbon components or fraction of a gasoline pool are effectively upgraded.
A further aspect of this invention is to provide a process for upgrading a gasoline pool wherein C.sub.6 paraffinic hydrocarbons are upgraded in a process stage other than in a reformer.
Other objects and advantages of this invention will become more apparent from the discussion and examples hereinafter expressed.